Soy proteins are valuable food ingredients due to their high nutritional value. The health benefits of soybeans and soy products have been known and well documented for some time. Soybeans and other soy proteins have been widely accepted in Asia for centuries and are one of the principal sources of protein in a traditional Asian diet. Despite this, soy protein has not been as widely accepted for use in food products in the United States, primarily due to consumers' objections to the flavor of soy. In recent years, however, soy-based products have enjoyed a great increase in popularity as people have become more health-conscious.
Soybeans, and soy proteins in general, are a nutrient-rich and inexpensive vegetable protein source with a variety of health benefits. The primary health benefit of soy protein is its ability to lower cholesterol levels. Soy proteins lower total cholesterol and LDL cholesterol (“bad” cholesterol) and decrease blood clotting, which reduces the risk of heart attack and stroke. Soy proteins also provide antioxidants, reduce artery-clogging plaque, improve blood pressure and promote healthy blood vessels, which protect the body from free radical damage, boost the immune system, and lower the risk of atherosclerosis (the hardening of the arteries), heart disease, and hypertension (high blood pressure). In fact, the Food and Drug, Administration (FDA) has granted a Cardiac Vasular Disease (CVD) soy protein health claim for its cholesterol-lowering ability. In addition to a tendency to lower cholesterol levels, soybeans have recently been linked with, or suggested as having a possible role in, inhibiting the development of cancer. Fiber in soy protein materials protects the body from many digestive related cancers, such as colon and rectal cancer, while isoflavones in soy materials may protect the body from hormone-related cancers, like breast, uterine, and prostate cancer. Soy protein also contributes to bone health and longevity by enhancing the body's ability to retain and absorb calcium in the bones, thus reducing effects of osteoporosis. Isoflavones in soy materials also help the body regulate estrogen when the hormone is declining or fluctuating, which helps alleviate symptoms of menopause in women. Additionally, soy protein contains an amino acid profile that is among the most complete of all vegetable protein sources, and resembles, with the exception of the sulfur-containing amino acids, the pattern derived from high-quality animal protein sources. Soy also contains many vitamins, minerals, and phytochemical compounds, such as isoflavones, that work together to create other health benefits. Thus, due to the variety of health benefits of soy protein, efforts have been made to incorporate soy into a wide variety of foods.
Soy protein isolate (SPI), soy protein concentrate (SPC), and soy flour (SF) are major sources of soy protein. Soy protein concentrates and soy protein isolates are the most highly refined commercially available soy protein-containing products. Both soy protein concentrates and isolates are processed to increase soy protein content. Soy protein isolate contains approximately ninety percent or more soy protein by weight, but is also the most expensive of the three major sources of soy protein. Soy protein concentrate contains approximately sixty-five to eighty percent soy protein by weight and has a cost which is intermediate between lower cost soy flour and more expensive soy protein isolate. Soy flour contains about forty-five to fifty-five percent soy protein by weight and is the least expensive of the three major sources of soy protein. Soy flour also has substantial amounts of carbohydrates and relatively small amounts of oligosaccharides (e.g., raffinose and stachyose) which can be removed using an α-galactosidase enzyme.
It is generally desirable to reduce the oligosaccharide content of soy products because raffinose and stachyose oligosaccharides induce intestinal
In addition to its health benefits, soy protein is also known to have emulsifier functionality. An emulsifier allows the combination or mixture of two ingredients that normally do not easily mix. Generally, two or more immiscible liquids, such as oil and water, may form an emulsion merely upon shaking, but the emulsion is very unstable and the liquids quickly separate into separate layers. An emulsifier works by coating droplets of one liquid so that the droplets may remain suspended in the other liquid. For example, in salad dressings an emulsifier allows the production of a stable mixture of oil and water, two materials which would normally separate into two separate layers when mixed. It is desirable for an emulsifier to maintain the emulsion for a long period of time without undergoing separation into layers or components. As an emulsifier, soy protein surrounds an oil droplet and allows the droplet to remain suspended in water, thus allowing the formation of a stable oil-in-water emulsion.
Currently, egg yolk and whole eggs are important ingredients used in starch-based salad dressing products (e.g., MIRACLE WHIP™ from Kraft Foods, Northfield, Ill.). The proteins and lecithin in the whole egg or egg yolk function as emulsifiers in the salad dressing. The whole egg or egg yolk stabilize the emulsion droplets, while the gelatinzed starch base stabilizes the aqueous phase in which the spices, sweeteners, and remaining soluble proteins and other electrolytes are suspended. Generally, the content of protein in whole egg and egg yolk are thirteen percent and sixteen percent, respectively. Both whole egg and egg yolk are susceptible to microbial contamination and, thus, whole egg or egg yolk salted with ten percent salt is regularly used in place of pure whole egg or egg yolk. Refrigeration of the salted whole egg or egg yolk is required and, even when refrigerated, the shelf life of the whole egg or egg yolk is relatively short. These factors, as well as the high purchase cost of whole egg and egg yolk emulsifiers, make their use in salad dressings very costly.
In comparison, soy flour is an inexpensive and protein-rich ingredient. Soy flour also does not contain cholesterol and has a variety of health benefits, as discussed above. Additionally, soy flour has a relatively long shelf life. Therefore, utilization of soy protein, especially soy flour, to replace other costly emulsifiers would allow significant cost savings in the production of food products.
The replacement of whole eggs or egg yolk with soy flour in starch-based salad dressing products could result in healthier products and significant cost savings. However, due to the solubility, texture, and flavor problems associated with soy protein, relatively unprocessed soy protein materials, such as soy flour, have not been widely used in food products to date.
Examples of efforts to utilize soy proteins in salad dressings include U.S. Pat. No. 4,163,808 (use of soy proteins as the sole or dominant emulsifier in an imitation mayonnaise and salad dressing); U.S. Pat. No. 4,304,795 (use of soybean protein in a semisolid egg yolk-free dressing); U.S. Pat. No. 4,322,344 (use of a chemically phosphorylated soy protein in a salad dressing); U.S. Pat. No. 4,426,395 (use of a partial hydrolyzate of alcohol denatured soybean protein as an emulsifier); U.S. Pat. No. 4,757,007 (a low solubility hydrolyzed soy protein which has emulsifying properties); and U.S. Pat. No. 6,090,432 (use of tofu as an ingredient in a salad dressing).